Retention Testing Methodology for STTRAM

Spin-torque transfer RAM (STTRAM) is a promising memory technology due to its low power, high speed, and robustness. However, the shift of retention time from a few years to a few microseconds due to temperature, thermal, statistical, and stochastic variations makes retention testing nontrivial and time consuming. This article analyzes the impact of process variation, temperature, and disturb current on data retention. It provides a design-for-test (DFT) solution to reduce the test time by incorporating a weak write test mode to effectively screen the weak bits from other strong bits. Additionally, it presents an at-burn-in technique and an after-burn-in technique to test data retention. These techniques compress the retention time test to the order of microseconds.